1. Field of the Invention
This invention relates to a liquid crystal composition for liquid crystal display. More particularly, it relates to a liquid crystal composition used for a display element using TN (twisted nematic) mode or STN (super-twisted nematic) mode, and a liquid crystal display element using the same.
2. Description of the Related Art
Liquid crystal display element (LCD) utilizes the optical anisotropy and the dielectric anisotropy, and those utilizing nematic liquid crystalline phase among liquid crystal phases have been most often practically used. LCD makes possible, lower power consumption, smaller size and lighter weight, as compared with CRT (braun tube), etc.; hence it has begun to be used for handy type electronic calculator, digital watch, etc. and its application to word processor, television, meter panel for cars, etc. have also been broadened.
As liquid crystal substances expected as a material used for LCD, those exhibiting liquid crystal phases within a temperature range as broad as possible, around room temperature are desired, and they should be sufficiently stable to environmental factors used and have sufficient physical properties for driving display elements. At present, however, those satisfying these conditions as a single compound have not yet been found; hence several kinds of liquid crystal compounds are mixed or further a non-liquid crystal compound is mixed therewith to prepare liquid crystal compositions having various characteristics, and such compositions have been used as a material for LCD.
For example, as the characteristics of liquid crystal compositions sought for TN mode, the following ones have been required:
1) the nematic-isotropic phase transition point is high; PA1 2) a suitable optical anisotropy can be taken depending upon the cell thickness of LCD; and in the case of STN mode, in addition to the above characteristics, it is required PA1 3) the voltage-transmittance curve is steep. PA1 A liquid crystal composition which comprises PA1 the proportion of the first component in the composition is 3 to 70% by weight; that of the second component is 3 to 70% by weight; and that of the third component is 3 to 70% by weight. PA1 3 to 50% by weight of a first component containing at least one compound chosen from among a group of compounds expressed by the above formula (1a); PA1 3 to 50% by weight of a second component containing at least one compound chosen from among a group of compounds expressed by the above formula (3); and PA1 3 to 70% by weight of a third component containing at least one compound chosen from among a group of compounds expressed by the above formula (6), at least one compound chosen from among a group of compounds expressed by the above formula (7) and at least one compound chosen from among a group of compounds expressed by the formula (8). PA1 3 to 50% by weight of a first component containing at least one compound chosen from among a group of compounds expressed by the above formula (1a); PA1 3 to 50% by weight of a second component containing at least one compound chosen from among a group of compounds expressed by the above formula (2), at least one compound chosen from among a group of compounds expressed by the above formula (4) and at least one compound chosen from among a group of compounds expressed by the formula (5); and PA1 3 to 70% by weight of a third component containing at least one compound chosen from among a group of compounds expressed by the formula (6), at least one compound chosen from among a group of compounds expressed by the formula (7) and at least one compound chosen from among a group of compounds expressed by the formula (8). PA1 3 to 50% by weight of a first component containing at least one compound chosen from among a group of compounds expressed by the formula (1a); PA1 3 to 50% by weight of a second component containing at least one compound chosen from among a group of compounds expressed by the formula (2), and at least one compound chosen from a group of compounds expressed by the formula (5); PA1 3 to 70% by weight of a third component containing at least one compound chosen from among a group of compounds expressed by the formula (9). PA1 3 to 50% by weight of a second component containing at least one compound chosen from among a group of compounds expressed by the above formula (2); and PA1 3 to 70% by weight of a third component containing at least one compound chosen from among a group of compounds expressed by the above formula (6) and at least one compound chosen from among a group of compounds expressed by the above formula (8). PA1 3 to 50% by weight of a first component containing at least one compound chosen from among a group of compounds expressed by the above formula (1a); PA1 3 to 50% by weight of a second component containing at least one compound chosen from among a group of compounds expressed by the above formula (2), PA1 at least one compound chosen from among a group of compounds expressed by the above formula (4), and PA1 at least one compound chosen from among a group of compounds expressed by the above formula (5); and PA1 3 to 70% by weight of a third component containing at least one compound chosen from among a group of compounds expressed by the above formula (6), PA1 at least one compound chosen from among a group of compounds expressed by the above formula (8), and PA1 at least one compound chosen from among a group of compounds expressed by the above formula (9). PA1 3 to 50% by weight of a first component containing at least one compound chosen from among a group of compounds expressed by the above formula (1a); PA1 3 to 50% by weight of a second component containing at least one compound chosen from among a group of compounds expressed by the above formula (2) and at least one compound chosen from among a group of compounds expressed by the above formula (4); and PA1 3 to 70% by weight of a third component containing at least one compound chosen from among a group of compounds expressed by the above formula (6), PA1 at least one compound chosen from among a group of compounds expressed by the above formula (7) and at least one compound chosen from among a group of compounds expressed by the above formula (8). PA1 a case where it consists of at least one compound chosen from among a group of compounds expressed by the above formula (2).
An example of such liquid crystal compositions is a liquid crystal composition disclosed in Japanese patent application laid-open No. Hei 1-156392 wherein an LCD having a steep voltage-transmittance curve and a good contrast has been sought.
In recent years, energy-saving has been called for and demand for small type, light-weight, portable products such as electronic note-book, IC card, etc. has increased; hence as a development theme directed to LCD, low power consumption and low voltage driving have been mentioned. Further, it has raised an important problem to reduce an inferior display such as contrast insufficiency and cross-talk within a service temperature range. As the liquid crystal material, it has been required to reduce the threshold voltage in the electrooptical characteristic and reduce the temperature-dependency of the threshold voltage.
However, the liquid crystal composition disclosed in Japanese patent application laid-open No. Hei 1-156392 exhibits a high threshold voltage and an inferior temperature dependency of the threshold voltage; hence the liquid crystal composition is insufficient to be used for LCD of small type, light weight, portable product, etc., restricted in the driving electric source.
As described above, it is the present status that a product exhibiting a low threshold voltage and a superior temperature dependency of the threshold voltage has been earnestly desired.